A large number of medical cements of various compositions have previously been proposed for use in living bodies. Among all, calcium phosphate cements for living bodies have an advantage in that, this kind of cement upon hardening changes into a bioactive hydroxyapatite, and hence results in a hardened cement having excellent bioaffinity.
Many of these calcium phosphate cements for living bodies comprise tetracalcium phosphate as the main component. For example, U.S. Pat. No. 4,612,053 discloses cements comprising tetracalcium phosphate and calcium hydrogen phosphate as the main components. It is also known that the hardening properties of these calcium phosphate cements widely vary depending on the amount of liquid employed in the step of kneading. That is, the hardening time is shortened while the strength of the hardened body is elevated with a decrease in the kneading liquid employed (1990, Orthopaedic Ceramic Implant Vol. 10, p. 43-47).
When a kneading liquid is used in a small amount, however, the kneaded body becomes highly viscous and thus the handleability is deteriorated in the step of kneading. When such a cement is filled into a defective site of a bone, etc., cracks or voids are frequently formed therein and thus the strength of the hardened body is deteriorated. To obtain a kneaded body having sufficient handleability, it is therefore necessary to minimize the amount of the kneading liquid. In the field of cements for industrial use, on the other hand, it is known to use water reducing agents, AE water reducing agents, etc. to decrease the amount of kneading liquids while preventing the deterioration in the handleability. However, it is undesirable to apply these water reducing agents to cements to be used in living bodies, since no attention is paid to the safety in vivo with respect to these water reducing agents.
When such a calcium phosphate cement is kneaded and then immediately brought into contact with a pseudo body fluid, water penetrates into the kneaded body and disintegrates the same. Thus, there arise some troubles that the cement paste fails to retain its shape and inflammatory reactions are caused. Consequently, two different methods have been used to apply the cement to a body part where body fluids are present in a large amount. The first method is to apply a cement paste, not immediately after kneading, but instead after it has hardened to some degree. The second method is to apply the cement paste after removal of the body fluids from the body part and after homeostasis, etc. However, the cement paste which has hardened to some degree is difficult to handle and has poor handleability in, for example, filling up a defective part.